An electrochemical measuring cell for detecting hydride gases such as phosphine and arsine is disclosed in U.S. Pat. No. 5,128,018. In this known measuring cell, a measuring or working electrode, a reference electrode and an auxiliary electrode are mounted in an electrolyte chamber of a measuring cell housing. The electrolyte chamber is closed off with a gas permeable diffusion membrane toward the ambient which contains the gas sample to be measured having the hydride gas to be detected. Sulphuric acid with catalyzing additives is used as an electrolyte.
Although the known measuring cell is characterized by a high sensitivity, cross sensitivities are present relative to a series of other gases. In specific applications, these cross sensitivities are especially disturbing or can lead to false alarms. In addition to phosphine and arsine, the known measuring cell also reacts to NO.sub.2, H.sub.2, C.sub.2 H.sub.2, SO.sub.2, H.sub.2 O.sub.2 and O.sub.3.